Weather Encounter Leads to In-Flight Breakup
An airplane sustained an in-flight breakup after encountering weather while operating under instrument flight rules (IFR). The flight was being radar vectored to the ILS final approach course at an altitude of 3,000 feet when the breakup occurred.
Wreckage Examination
The debris path extended approximately 1/4 mile in length. The first pieces of wreckage to fall were the left wing tip and the outboard half of the left and right horizontal stabilators. The horizontal stabilators exhibited permanent downward deformation at the separation points. The wings showed both upward and downward permanent deformation of the spars and other structural elements. Fracture surfaces at the separation points for the wings and stabilators were consistent with structural overload.
Weather Conditions
The National Weather Service (NWS) had issued SIGMETs and AIRMETs for occasional severe turbulence, strong gusty winds, low-level wind shear, and occasional severe rime to mixed icing in clouds. These advisories were valid before the pilot's departure and covered the timeframe of the flight. NWS weather radar depicted moderate intensity echoes extending over the accident site.
While en route at 1219, the pilot requested current destination weather from the center controller and received a METAR report of 10 miles visibility with broken layers at 4,000 and 20,000 feet. Shortly after that observation, the destination conditions rapidly deteriorated, including lowering ceilings, strong and gusty winds, and moderate to heavy rain showers.
Approximately 30 minutes before the accident, the destination weather included winds gusting to 21 knots, scattered clouds at 3,800 feet, and a broken layer at 10,000 feet. A special observation issued about 5 minutes before the accident indicated winds gusting 14 to 19 knots, visibility 2 miles in moderate rain and mist, a broken ceiling at 2,800 feet, and overcast at 5,000 feet. Rain had begun about 15 minutes earlier.
Five minutes after the accident, another observation reported winds gusting to 21 knots, visibility 1.5 miles with moderate rain, and broken and overcast ceilings at 2,100 feet and 4,700 feet, respectively. The crew of a Boeing 757 making the approach 10 minutes after the accident reported a 45-knot crosswind shear at 100 feet and light to moderate turbulence throughout the approach.
An analysis of weather conditions at the time of the accident, including radar and satellite sensor imagery, disclosed strong weather echoes near the accident site with embedded areas of intense to extreme echoes. Cloud tops were in excess of 33,000 feet. The analysis indicated that several low-level wind shear layers were present with moderate to severe turbulence.
Pilot Actions
There is no record that the pilot requested or received a preflight weather briefing.